The present invention relates to the field of exhaust air systems for buildings and/or other enclosed areas, and more particularly, to exhaust discharge nozzles configured to be attached to the outlets of exhaust fans, exhaust ducts and/or stacks, and similar exhaust type equipment/devices and are specifically designed to be installed in the outdoor ambient. The device is designed with a constriction at the outlet to accelerate the exhaust effluent at a high velocity into the atmosphere.
The present invention is related to the disclosure of U.S. patent application Ser. No. 13/067,269, which is incorporated herein by reference.
The application of discharge nozzles at the exit point of exhaust systems enhances the performance capability with the specific intent of maximizing the exhaust/effluent dispersion into the upper atmosphere of the unwanted contaminated air and/or effluent gases and vapors from buildings, rooms, and other enclosed spaces. They are able to provide a superior alternative to conventional tall exhaust stacks which are costly to construct and are visually unattractive by today's standards. Properly designed nozzles are capable of propelling high velocity plumes of exhaust gases to heights sufficient to prevent stack downwash and disperse the effluent over a large upper atmospheric area so as to avoid exhaust contaminant re-entrainment into building ventilation intake zones.
A further development of the constrictive exhaust nozzle design is the type of nozzle that employs the Venturi effect to draw additional ambient air into the primary effluent stream. The venturi type nozzle can further be described as an aspirating, or induction type, as related to conventional technological description for this type nozzle. The additional induced air volume dilutes the primary exhaust gases at/near the nozzle as the combined mixed air volumes are released into the atmosphere. Also, with this exhaust-air mixture volume increase, the discharged gas is expelled at a higher velocity, achieving a greater plume height. The underlying effect of greater volume at greater discharge velocity is increased effluent momentum, which assists with the effluent disbursement into the atmosphere.
One of the limitations of the prior art in this field relates to the performance of the nozzle in a crosswind. Crosswinds not only affect the external plume height, in accordance with the Briggs equations, but they can also interfere with and limit ambient air entrainment into the nozzle, thereby impairing the performance at the nozzle discharge. The current industry test standard, AMCA 260-07, is a static test based on a zero crosswind velocity, which does not reflect the true application of these devices. Therefore, the industry has not yet addressed the effect of crosswind “blow through” that can take place. The present invention addresses this prevalent problem to which the prior art is susceptible. FIG. 1 illustrates the significantly degraded performance of one of the prior art induction nozzles in a crosswind (15 mph), as compared with the present invention, which enables substantially unimpaired performance in the equivalent crosswind.
Among the features of some of the prior art nozzles that render them particularly susceptible to crosswind “blow through” is the interconnection of their induction ports. Several prior art designs use a bifurcated frusto-conical nozzle with a “see-through” central passive zone that functions as the inlet for induced air flow. In the static condition (no crosswind), as illustrated in FIG. 2, ambient air enters the interconnected induction ports and is discharged through the nozzle outlet along with primary air. But in the dynamic condition (with crosswind), as shown in FIG. 3, this “see-through” design allows crosswinds to freely “blow through” the nozzle's passive zone instead of entering the aspiration air column and mixing with the primary exhaust discharge. Such crosswind pass-through impairs the performance of the nozzle by diminishing induction flow and reducing the nozzle discharge volume, thereby also reducing plume height.
Examples of nozzles with “see-through” interconnected induction ports, of the type illustrated in FIG. 4A-C, are disclosed in the U.S. patents of Andrews (U.S. Pat. No. 4,806,076), Kupferberg (U.S. Pat. No. 5,439,349), Secrest et al. (U.S. Pat. No. 6,112,850), and Tetley et al. (U.S. Pat. No. 6,431,974). The patent of Andrews teaches a bifurcated frusto-conical central nozzle which branches into dual arcuate primary exhaust air discharge outlets circumferentially disposed around a central “see-through” passive zone, which is the principal source of induced ambient air. The mixing of exhaust flows with induced ambient air takes place peripherally above the nozzle outlets. The wind band is not full-length over the nozzles and does not shield the passive zone ambient air inlets from crosswind disruption. Moreover, the interconnected “see-through” induced air inlets are subject to crosswind pass-through, which impairs nozzle performance, as explained above. The short wind band mounting brackets do not channel air into the induction zone inlets. The patents to Kupferberg and Secrest et al. are variations of the Andrews bifurcated “see-through” design.
The U.S. patent of Tetley et al. (U.S. Pat. No. 6,431,974) teaches the Andrews “see-through” design with multiple nested wind band sections in vertically spaced relation over the arcuate exhaust air outlets. This configuration sets up a succession of extra-nozzle peripheral mixing zones, as opposed to the single mixing zone of Andrews, Kupferberg and Secrest et al. Andrews' deficiencies with respect to full-length wind band and mounting bracket also apply to Tetley et al.
In the “Aspirating Induction Nozzle” described in U.S. patent application Ser. No. 13/067,269, a full-length wind band, extending from below the induction port inlets to above the nozzle discharge outlet, is used to protect the induction port inlets from crosswind disruption. The “Aspirating Induction Nozzle” design also uses full-length wind band mounting brackets, between the nozzle and the wind band, to form individual vertical air passageways for each of the ambient air induction ports, thereby preventing crosswinds from circumventing and disrupting the vertical flow of induced ambient air into the primary effluent flow. As depicted in FIG. 4C, the wind band design taught by the prior art is deficient in both of these aspects. The prior art wind band does not extend over the induction port inlets, thereby leaving them exposed to crosswind “blow through.” Moreover, the prior art wind band mounting brackets are too short to form effective vertical air passageways for the induction ports.